m 



UNITED STATES DEPARTMENT OF AGRICULTURE 




Washington, D. C. 



PROFESSIONAL PAPER 



December 10, 1917 



WALNUT BLIGHT IN THE EASTERN UNITED 

STATES. 

By S. M. ^loMuBRAN, 
Assistant Pathologist, Office of Fruit-Disease Investigations. 



CONTENTS. 



Page. 

Importance of the disease 1 

History of walnut blight 2 

The disease in the Eastern State;;... 4 



Page. 

Time of infection 5 

Control of walnut blight , 5 

Summary,...,.,,,.... 6 






IMPORTANCE OF THE DISEASE. 

The growing of the Persian (English) walnut in the eastern half 
of the United States is receiving increasing attention and arousing 
the interest of many. Persian walnut trees, mainly seedlings, either 
isolated or in small groups or orchards, are by no means uncommon 
in the States east of Lake Michigan and the Wabash River below the 
latitude of New England. An indication of the number of such trees 
now growing in this part of the country was contained in an address 
by Prof. F. N. Fagan, of State College, Pa., delivered before the 
Northern Nut Growers' Association in 1915, in which the statement 
was made that as the result of a recent survey by that college the 
"location of some 1,500 or 2,000 bearing trees'' had been ascertained 
in that State. While there has been no effort to make a similar 
survey in other Eastern States, so far as the writer is informed, his 
personal knowledge and that of associates in the Bureau of Plant 
Industry indicates practically the same proportion of Persian walnut 
trees in the States of New York, Delaware, New Jersey, and Mary- 
land. Isolated trees are known in lower Connecticut, southern Michi- 
gan, Ohio, and Virginia. Several eastern nurseries are now spe 

Note. — This bulletin is intended particuiarly for all engaged in propagating Per 
walnuts In those portions of the United States east of the Eocky Mountains. Ifi' 
of scientific interest to plant pathologists. 
13187''--17— BuU. Gil 



^'o^ograph 



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2 BULLETIN 611, U. S. DEPARTMENT OF AGRICULTURE. 

cializing in the growing of young trees for general planting. These; 
facts, together with the increasing volume of correspondence re- 
ceived by the Department of Agriculture relative to walnut diseasesj 
and the known occurrence of the walnut blight, or bacteriosis, in the! 
eastern United States, make it desirable to publish at this time a! 
resume of the history of this disease and its present status in the' 
section specified, to the end that difficulties and disappointments! 
may be avoided. 

Commercial walnut growing in the United States may be said to 
have had its origin on the Pacific coast. At present the principal 
production of Persian walnuts in this country is from a few counties 
in southern California, although within recent years there has 
been extensive planting in the San Joaquin Valley, the Sacra- 
mento Valley and adjacent valleys of northern California, and in 
the Willamette Valley of western Oregon. To a con-siderable extent 
this walnut is now being planted by amateurs and experimenters in 
other States, especially Arizona and New Mexico. As a result of 
this situation, systematic studies of the species and its varieties, its 
cultural requirements, diseases, and insect pests have largely been 
confined to the West, and except as analogies can be drawn there is 
little in agricultural literature that will be of assistance to a prospec- 
tive grower in the eastern United States. 

During the seasons of 1910, 1911. and 1914 specimens of diseased 
nuts were received by the Bureau of Plant Industry from points, in 
Maryland, I^ouisiana, Pennsylvania, Virginia, and Delaware and 
determined ])y Mr. M. B. Waite, Pathologist in charge of the Office 
of Fruit-Disease Investigations, to be affected with the so-called 
walnut blight, or bacteriosis. During the summer of 1916 an effort 
was made by the writer to determine the extent of the occur-, 
rence and the seriousness of this trouble in the eastern Unit^^d 
States, as it appeared to be the most serious disease with which the 
industry now has to contend in this part of the country. Blighted 
huts were found at practically all points at which bearing waliiut 
trees were examined, and reports from other sections indicate that 
the presence of this disease is more or less general in the entire 
eastern district. 

HISTORY OF WALNUT BLIGHT. 

In 1901 Pierce ^ reported a walnut disease due to a bacterium which 

had at that time become established in the seedling orchards of 

southern California. He stated that it was highly pathogenic on 

oung nuts, leaves, and tender twigs and frequently caused serious 

Herce, N. B. Walnut bacteriosis. in Bot.Gaz., v. 31, no. 4, p. 272-2<b. .1901 



t)^ Of jO, 



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WALNTJT BLIGHT IN THE EASTERN UNITED STATES. 3 

■l6ss of young nuts. His paper gives a number of the characteristics 
of the organism in pure culture, and his work has subsequently been 
corroborated by Clayton O. Smith, of the Whittier Station in Cali- 
fornia, and the writer, in the eastern United States. Pierce pro- 
posed the term " bacteriosis " as being a suggestive name for the 
disease, though by growers the malady is commonly known and 
spoken of as walnut blight, which may be considered its common 
name. The disease-producing organism is now known as Bacterium 
fuglandis (Pierce) Erw. Smith. ^ Since the publication of Pierce's 
paper reports b}^ other writers have appeared from time to time, 
the most valuable contribution being Bulletin No. 231 of the Cal- 
ifornia Agricultural Experiment Station.^ The work reported in this 
paper, which extended over a period of some years, largely con- 
firmed Pierce's studies and greatly augmented the existing knowl- 
edge of the disease-producing organism and its relation to its host. 

A brief quotation will serve to indicate the seriousness with which 
this disease is regarded on the Pacific coast and the gravity with 
which it should be considered by present and prospective growers 
elsewhere. 

This is by far tlie most important trouble affecting tlie walnut in California. 
So serious has been this disease that the loss of a large portion of the crop has 
in some cases been charged to this source, legislatures have made special ap- 
propriations for its investigation, and the growers have offered a large reward 
for a practical remedy. 

At the same time the losses directly attributable to blight have been extremelj: 
large. One significant fact in tliis connection is that while the walnut acreage 
in southern California has multiplied many times during the past decade 
(1902-1912), the total walnut crop has increased very little during this time. 

This loss or failure of the crop to increase has not been entirely attribtitable 
tO' blight, yet it has certainly been due to the disease much more than to any 
other one factor.' 

Until a few years ago walnut bacteriosis had been definitely known 
to occur only on the Pacific coast and in New Zealand. In 1913 
Waite* reported the disease as occurring in the Eastern States. 
He stated : 

The California walnut bacteriosis has turned u)> at various points in the 
East. The twig-blight form of this disease is also prevalent in various States. 
The walnut blight, or bacteriosis, is therefore to be figured with in planting the 
Persian walnut in the East. ... It occurs in Texas and Louisiana, and I 
think we have it in or near Buffalo, N. Y., and in New Jersey, so if I were 

1 Smith, E. F. Bacteria in Relation to Plant Diseases, v. 1, p. 171. Washington, 
D. C. (Carnegie Inst., Washington, Pub. 27.) 

^SmJth, R. E., Smith, C. 0., and Ramsey, H. J. Walnut culture in California. Walnut 
blight Cal. Agr. Exp. Sta. Bui. 231, p. 113-.S98, 90 fig. 1912. 

8 Smith, R. E., Smith, C. O., and Ramsey, H. J, Op. cit. 
' * Waitei M. B. The diseases of nut trees. In Rept. Proc. 4th Ann. Meeting, Northern 
Nut Growers' Assoc, 1913, p. 56. 1914. 



4 BULLETIN 611, U. 3. DEPABTMENT OF AGRICULTURE. 

planting extensively I should expect that disease to be serious. That would be 
ray forecast of the matter. The humidity and cloudy weather in the East 
ought to be moi-e fsivorable to the disease than the climnte of California. 

There is no reason to suppose that blight will not appear wherever 
Persian walnuts are grown. 

THE DISEASE IN THE EASTERN STATES. 

During the first week in June, 1916, a trip was made by the writer 
to various points in Delaware, New Jersey, and Pennsylvania where 
bearing walnut trees were known to be located. On practically every 
tree that had a crop the nuts were found to be spotted in a manner 
very characteristic of bacteriosis (PL I). The lesions at this time 
were small and superficial in character, rarely extending more than 
2 to 3 millimeters (about one-tenth of an inch) into the husk. A 
number of specimens were collected and cultures obtained. 

The technique used consisted in washing the nuts with soap and 
water, sterilizing the surface with an alcoholic solution of mercury 
bichlorid for five minutes, and then washing in distilled water. 
After this treatment the epidermis of the diseased spots was removed 
carefully with a sterile scalpel and bits of subepidermal tissue trans- 
ferred to tubes of melted beef agar, agitated, further diluted in a 
second and third tube of the same media, and poured into Petri 
dishes. About 15 attempts were made, in practically all of which 
bacterial colonies of a similar type appeared on the plates in from 
two to four days, and the plates from the third dilutions usually 
contained colonies which were so few as to allow transfers to be 
made to tubes without difficulty. During the first week in August 
a series of inoculations was made on the nuts and twigs of a certain 
mature tree at Lancaster, Pa., which was said to be a seedling of 
Rush. The husks of 24 young nuts entirely free from any trace of 
the disease were inoculated (1) by spraying with a suspension of 
the germs in rain water, (2) by smearing on the culture, and (3) 
by puncturing with an infected needle. Several untreated nuts were 
tagged as controls. At the same time five young, tender, growing 
twigs .5 to 10 millimeters in diameter were inoculated with the germs 
about 6 inches from the tips by making several punctures in each 
with an infected needle ; one twig was punctured with a sterile needle 
as a control. The organisms used in these experiments were all from 
pure cultures on beef agar and obtained as previously described. 

A month later (Sept. 5, 1916) it was found that 21 of the 24 nuts 
inoculated had developed the disease and 3 showed no trace of it; 
the untreated nuts were perfectly clean. Of the five twigs inocu- 
lated, all had developed cankers from 5 to 10 mm, in length and from 
2 to 5 mm. in width. Plate II shows one of the nuts 30 days after 



Bui, 61 1, U. S. Dept. of Agriculture. 



Plate I. 




Bui. 61 1, U. S. Dept. of Agriculture. 



Plate II. 




Diseased and Healthy Persian Walnut Twigs and a Nut Affected with 

Walnut Blight. 

A nnd n typical cjukers produced on twigs in one mouth's time by needle punctures from 
pure culture; C, a control twig punctured with a sterile needle; D, a diseased nut one 
monlh alter being inoculated from a pure culture by a needle puncture. 



WALNUT BLIGHT IN THE EASTERN UNITED STATES. 5 

inoculation b)^ needle puncture and two inoculated twigs having 
characteristic cankers. The control, which was punctured with a 
sterile needle, is shown at the right. The needle punctures in the con- 
trol barely showed at this time, 30 days after inoculation. 

Subsequently the organism was reisolated from a number of these 
inoculated nuts, and the cultural studies so far made from these 
isolations coincide with those made by Smith ^ and by Pierce.* 

TIME OF INFECTION. 

During the season of 1916 infection apparently took place about 
the last of May in the cases under observation. At this time the 
nuts were very well developed, approximately three-fourths to 1 
inch in diameter, and although there was a slow increase in the area 
of the infection points through July and some coalescing of these 
spots to form larger ones, the disease did not begin to work 
deeply into the tissues until about the middle of August, by which 
time the shell had formed and hardened. By the end of the 
season the husks had become black, watery, and rotten, staining 
the shells and clinging to them when allowed to dry. The develop- 
ment of the nuts did not seem to be affected materially, if at all. 
The growers interviewed were unanimous in stating that infection 
was usually late and that no material shortage of crop resulted there- 
from. However, the former part of this statement probably could 
be applied only to the time at which the infection became so evident 
as to attract the attention of ordinary observers. 

In the California orchards the greatest loss from infection occurs 
at or near blooming time. Infection is serious in proportion as the 
weather is moist at that time. A dry, clear spring means little, if 
any, blight, whereas serious infection is associated with moist, foggy 
spring weather. The disease as observed in 1916 in Pennsylvania, 
Delaware, and the District of Columbia resembled closely the severe 
late infections described by Smith.^ 

CONTROL OF WALNUT BLIGHT. 

Various attempts to control this disease by spraying and by soil 
applications have been made in California, and although some suc- 
cess has attended the spraying experiments it has not been of such 
degree as to extend any material encouragement to the commercial 
orchardist. That spraying will be of no value under eastern condi- 
tions can not be assumed from this fact, however, owing to the dif- 
ference in the infection periods previously referred to. Neverthe- 
less, spraying to control diseases of bacterial origin has never been 

* Smith, R. E., Smith, C. 0., and Etamsey, H. J. Op. clt. * Pierce, N. B. Op. cit 



6 BtrLLE'rijS' eiiy It. "s. Dfei>ARTM6>f'i' of AGRICULTDRE. 

§b successful as in the control of those due to fungi; until the efficacy 
Hi spraying may have become established, too much should not be 
expected from this method of control. 

A logical and seemingly practicable method of avoiding losses inci- 
dent to bacteriosis isin the possible development of immune or highly 
tesistant varieties. Work along this line is now under way on the 
Pacific coast, but it is not known that any varieties altogether re- 
sistant to blight or even practically immune to it have thus far been 
brought to light. However, among the many thousands of seedling 
trees on the Pacific coast and the hundreds in the eastern United 
States, it would not seem too much to presume that for general 
orchard planting blight-resistant and otherwise desirable varieties 
will yet be found. Whenever such varieties are discovered, arrange- 
ments maj^ be made with the Department of Agriculture for testing 
their susceptibility to this disease by means of inoculation experi- 
ments. Meanwhile, it is to be hoped that the planting of small com- 
mercial orchards and of trees for home use will be continued, as small 
groups of bearing trees over a wide range of territory will furnish 
valuable suggestions as to future commercial plantings. 

SUMMARY. ' 

Walnut blight, or bacteriosis, is distributed very generally through- 
but the eastern half of the country. Investigations by Mr. M. B. 
Waite and the writer have demonstrated its occurrence in Louisiana, 
the District of Columbia, Maryland, Delaware, Pennsylvania, and 
'New York, and there seems to be no reason to suppose that it will 
not occur wherever Persian wailnuts are grown in the United States. 

During the summer of 1916 pure cultures of the causal organism 
•were obtained from naturally infected nuts; inoculation experiments 
,were conducted in healthy tints and twigs, and these inoculations were 
uniformly successful in producing the disease. Cultural studies were 
conducted in the laboratory, and the results obtained corresponded 
with those reported by Pierce^ and by Smith.^ 

The writer's observations of this disease have covered one season 
only, and therefore definite conclusions as to its behavior under vary- 
ing seasonal conditions are not possible. It may be stated, however, 
that late infections were the rule during the season of 1916, and if 
this condition holds generally true from season to season it will con- 
stitute a striking difference between the behavior of the disease in the 
Middle Atlantic States and on the Pacific coast. 

Extensive experiments to control this disease by spraying have 
been conducted from time to tiipe in California, but the results ob- 
tained have never been entirely satisfactory. Here, again, the differ- 

* Pierce, N. B. Op. cit 'Smith, R. R, Smith, C. O.. and Ramsey, H. J. Op. cit 



WALNUT BLIGHT IN THE EASTERN UNITED STATES. 7 

f 

«nce in infection periods may alter results, but from the best infor- 
mation at present available it appears that the solution of the problem 
of the control of this disease rests in the development of immune or 
highly resistant varieties. Nurserymen and growers should be on the 
watch for such sorts as combine a high resistance to this disease with 
the other qualities necessary in a good commercial nut, and whenever 
such varieties are found they should be propagated. 

The wide planting of small lots of trees will furnish in the course 
of a few years valuable suggestions as to the requirements and range 
of the Persian walnut in the Eastern States, and should not be dis- 
couraged on account of blight. Although it is not possible at this 
time to say that this nut has large commercial possibilities in the 
section east of the Rocky Mountains, it is equally impossible to state, 
the contrary as the fact. It is well established, however, that there 
are now hundreds of seedling trees in New York, Pennsylvania, New 
Jersey, Delaware, and Maryland bearing nuts of more or less merit 
despite the presence of this disease, and apparently there is no reason 
why every farm and country home in this district should not have a 
small planting of these productive as well as highly ornamental trees. 



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The Bagworm, an Injurious Shade-Tree Insect, (Farmers' Bulletin 701.) 
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The Leaf Blister Mite of Pear and Apple. (Farmers' Bulletin 722.) 
The Oyster-Shell Scale and the Scurfy Scale. (Farmers' Bulletin 723.) 
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Orchard Barkbeetles and Pinhole Borers, and How to Control Them. (Farmers' I 

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The Death of Chestnuts and Oaks Due to Armillaria Mellea. (Department! 

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Walnut Aphides in California. (Department Bulletin 100.) 
Endothia Parasitica and Related Species. (Department Bulletin 380.) 
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